Since the advent of a resist for KrF excimer laser (248 nm), a pattern forming method utilizing chemical amplification is being used so as to compensate for sensitivity reduction due to light absorption. For example, in the positive chemical amplification method, a photoacid generator contained in the exposed area decomposes upon irradiation with light to produce an acid and, for example, in the baking process after exposure (PEB: Post Exposure Bake), an alkali-insoluble group contained in the photosensitive composition is changed into an alkali-soluble group by the catalytic action of the acid generated. Thereafter, development is performed using, for example, an alkali solution, whereby the exposed area is removed and a desired pattern is obtained.
As for the alkali developer used in the method above, various alkali developers have been proposed, but an aqueous alkali developer of 238 mass % TMAH (an aqueous tetramethylammonium hydroxide solution) is being used as the alkali developer for general purposes.
Furthermore, in view of enhancement of the pattern forming performance, such as enhancement of resolution in the positive chemical amplification method, it is being attempted to incorporate a group capable of decomposing by the action of an acid also into the photoacid generator (see, for example, Japanese Patent No. 3606291, JP-A-2006-201711 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) and JP-A-2007-199692).
Due to the miniaturization of a semiconductor device, the trend is moving toward a shorter wavelength of the exposure light source and a higher numerical aperture (higher NA) of the projection lens, and an exposure machine using an ArF excimer laser with a wavelength of 193 nm as a light source has been developed at present. As a technique for more enhancing the resolution, a method of filling a high refractive-index liquid (hereinafter sometimes referred to as an “immersion liquid”) between the projection lens and the sample (that is, an immersion method) has been proposed. Furthermore, EUV lithography of performing exposure to ultraviolet light at a shorter wavelength (13.5 nm) have been also proposed.
However, it is actually very difficult to find out an appropriate combination of a resist composition, a developer, a rinsing solution and the like necessary for forming a pattern with overall good performance. In particular, as the resolved line width of resist becomes finer, improvements of the line edge roughness performance of a line pattern and the in-plane uniformity of the pattern dimension are being demanded.
Recently, a pattern forming method using an organic solvent-containing developer has been developed (see, for example, JP-A-2008-281974, JP-A-2008-281975 and JP-A-2008-292975). For example, JP-A-2008-292975 discloses a pattern forming method including a step of applying, on a substrate, a resist composition capable of increasing the solubility for an alkali developer and decreasing the solubility for an organic solvent developer upon irradiation with an actinic ray or radiation, an exposure step, and a step of performing development by using an organic solvent developer. According to this method, a high-precision fine pattern can be stably formed.
However, the composition above is demanded to be more improved with respect to resolution, roughness performance and development time dependency.